3 Answers
3

Rav Herschel Shachter is quoted as saying that he determined many of these issues with the following test. He invited his (male) students over. When they stopped treating his daughters as little children and didn't pick up the daughters, the daughters were old enough to dress modestly, etc. I do not know how old this was, and given how old his daughters now are, I think the students are more inclined to pick them up metaphorically than literally.